Hydromechanical transmissions for tractors and the like typically include a plurality of gear ratios for providing a multitude of ground speeds for the tractor. Some tractors provide as many as 24 different forward speeds. Although 24 different speeds are provided, such a transmission develops relatively slow ground speeds with high torque. As an example, and although 24 different speeds are provided, the average difference in ground speed for the tractor between successive gear ratios is less than two miles-per-hour.
Such transmissions typically include several powershift clutches which are selectively operated to provide a respective one of the transmission's multi-gear ratios. Unlike other clutch mechanisms which operate in response to manipulation of a clutch pedal to disengage the transmission from a power source attendant to each shift or change in gear ratios, powershift clutches are typically hydraulically actuated clutch mechanisms which operate in response to pressurized fluid being directed thereto. The flow of pressurized fluid is directed to the various powershift clutches as a function of the position of an operator controlled shift lever.
The powershift clutches are arranged in the transmission such that a sequence of successively higher gear ratios, from neutral to an Nth speed, are obtainable as the shift lever is moved by the operator without disengaging the transmission from the power source. As such, each different position of the shift lever conditions the transmission to operate in a respective one of its multiple gear ratios. Each gear ratio corresponds to a different tractor speed. Naturally, efficient operation of the tractor is promoted by convenient transmission gear ratio selection.
As is known, rapid shifting of the transmission may result in rough shifts which can jolt the tractor, particularly if a shift is made under load. Because there are so many forward gear ratios and because of the relatively small difference in ground speeds, the tractor operator often finds it difficult to shift the transmission only one gear ratio at a time while progressively increasing the speed of the tractor up to the desired speed.
Understandably, the tractor operator often wants to reach the desired ground speed as fast as possible. As such, the tractor operator often times moves the shift lever too quickly thus imparting shift shock and its associated drawbacks to the tractor and often times "overshoots" the desired speed.